A crew was moving the BOP control POD from the bow to the aft of the moon pool in order to place it on the POD stand. The POD was lifted with one winch line with a sheave anchored directly above the POD. The weight was then transferred from that winch line to another winch line. The second winch line was lowered through the rig floor. During this procedure the utility winch in the moon pool was being utilized with a nylon strap choked to the POD arm so the POD could be pulled into position and lowered onto the POD stand. The nylon strap broke which allowed the POD to rotate and strike an employee.